Rumors of short battery life spans and high failure rates have scared off potential hybrid car buyers for years. Many hybrid customers ask if they'll eventually need to replace the battery pack and exactly how long they can expect the battery to last. Is it a matter of four years? Five years? Perhaps seven years?

The truth is, car companies guarantee their hybrid battery packs for the life of the car, which in recent years has been around 100,000 miles (160,934 kilometers) or more. And the warranties on the batteries generally last for eight years or even longer, in some cases. In other words, if the battery did fail for some reason while the car was still covered under warranty, the manufacturer would cover the replacement cost. The battery in the 2010 Toyota Prius, for instance, has a 10-year, 150,000-mile (341,402-kilometer) warranty.

While batteries are extending their life spans, they're also cutting back on the pounds. Read about batteries trimming down on the next page.